In the manufacture of a semiconductor device, semiconductor wafer (hereinafter, referred to simply as a wafer) serving as a substrate to be processed is exposed to a process gas capable of depositing or etching material on the substrate. The gas process is carried out, comprising the steps of: placing a wafer in a chamber; and supplying a reactant gas (corrosive gas), for example, a process gas containing halogen such as Cl, F, etc., to the chamber while decreasing pressure within the chamber. For example, a CVD process using Ti, TiN, W, etc., includes the steps of: heating a wafer, for example, to a temperature of 700 degrees C.; energizing a process gas into a plasma state if desired; and introducing the process gas (deposition gas) comprising a halogen-containing gas and a reducing gas into a chamber while decreasing pressure within the chamber to deposit a film.
However, when the process gas comprising a halogen-containing gas is used, Al, Fe, or Cu, etc., present in an Al alloy (e.g., JIS A 5052) or a stainless steel, of which an inner wall of a chamber or a member such as a showerhead mounted in a chamber is composed, reacts with by-product hydrogen halides such as HCl, HF, or the like, resulting from a gas reaction, thereby forming the corresponding metal halides. The metal halides are readily vaporized because of their increased vapor pressure in a chamber held at a reduced pressure and then diffuse towards the surface of the chamber, resulting in the formation of particles in the chamber or the introduction of particles into films during film deposition and thus the accumulation of metal contaminants on a wafer.
The metal contaminants tend to diffuse into a diffused layer in a silicon substrate through the bottom of a contact hole of a wafer and negatively impact transistor device performance, resulting in reduced breakdown voltage and poor quality ohmic contacts.
Recently, the pattern on a wafer have been further miniaturized, for example, the size of contact holes has been decreased to a level of about 0.13 micrometers in diameter and the depth of a diffused layer in a silicon substrate has been reduced to about 80 nm. Accordingly, as the depth of a diffused layer in a silicon substrate continues to shallow (shallow junction), the above-mentioned metal contaminants have an increasingly negative impact on transistor device performance and thus there is now an increased demand to provide a method for reducing metal contaminants. The reduction of metal contaminants is very important particularly in a metal film formation using a CVD method.
As a solution to the above problems, a method for coating the surface of chamber components, such as chamber wall and showerhead, with Ni, etc., has been disclosed in Patent document 1. When a nickel metal is in contact with halogen-containing gas, nickel halides might be formed. However, in this case, the nickel halides are low in vapor pressure and can hardly be vaporized and thus relatively smaller quantities of nickel halides are present as particles within a chamber, thereby reducing metal contaminants on a wafer.
However, even if the surface of the chamber components are made of nickel, there might be a problem in which nickel compounds nucleate to form particles when a process gas comprising NH3 and H2 is used to nitride a Ti film after deposition of Ti film on a member while the member is heated to a temperature as high as not less than 450° C.
[Patent Document 1] Jpn. Pat. Appln. KOKAI Publication No. 2003-313666